Infrared sensors have been widely used in sanitary wares, such as automatic faucets, automatic flushing urinals, toilet flushing devices, hot water spraying toilet seats, hand driers, and toilets provided with hot air fan.
Most conventional infrared sensors adopt an active infrared detection manner, in which an infrared emitter emits an infrared light at a specific wavelength, the infrared light is reflected from human body and the signal strength of the reflected signal is judged after being received by an infrared receiver, thereby to achieve automatic sensing and judgment. However, it is difficult to achieve the automatic sensing and judgment for substances with low infrared reflectivity (e.g., black clothing, hair, etc.). After the infrared light from the infrared emitter is reflected by such substances, only a small amount of infrared light is received by the infrared receiver. Since the intensity of reflected signal is not high enough, the sensor is unable to judge whether there exists an object, and therefore the sensing fails.
In order to solve the sensing failure problem of conventional infrared sensing sanitary ware, a distance detecting sensor is introduced into the field of sanitary automation. As shown in FIG. 1, a position detecting sensor, or called as position sensitive detector (PSD) is a photoelectric device that is sensitive to the position of incident light. That is to say, when the incident light irradiates at different positions on the photosensitive surface of the device, different electric signals can be outputted. The PSD achieves automatic detection and judgment by utilizing the triangular measurement principle with which distance can be measured accurately. As shown in FIG. 1, the light emitted from the light emitting source S.sub.1 is focused by a lens L1 and then projected onto the surface of an object O1 to be detected. The reflected light is focused by a lens L2 onto a one dimensional PSD (i.e., a receiving unit P1), and forms a light spot. Suppose the center distance between lens L1 and L2 is b, the distance from lens L2 to the surface of the PSD (i.e., focal length of lens L2) is f, and the distance from the light spot focused on the surface of the PSD to the center of lens L2 is x, it can be obtained based on the nature of similar triangles PAB and BCD that the distance DIS to be measured will be DIS=bf/x. Therefore, the distance of the object to be detected can be measured as long as the position coordinate x of the light spot on the PSD is obtained.
If it is detected that the distance of the object O1 falls within a preset range, the distance detecting sensor will control the operation states, including for example water output, flushing and etc, of the sanitary ware. Since the distance detecting sensor achieve the object of automatic detection by judging the distance between the object and the distance detecting sensor, it can effectively overcome the drawback of sensing failure of conventional infrared sensors.
However, there are some requirements for detection distance when such a distance detecting sensor is used. If the distance from the object to be detected to the distance detecting sensor is too close, the infrared light emitted from the light emitting source of the distance detecting sensor can't be focused onto the surface of the PSD, and therefore the detection will fail. For example, when such a distance detecting sensor is mounted on a faucet, if the hands of the user are too close to the distance detecting sensor, sensing failures happen easily.
Therefore, it is necessary to invent a distance detecting sensor and a method that can effectively overcome the drawback in the prior art.